Many wireless communications devices, such as cellular telephones, pagers, remote control devices, and the like, benefit from operating with physically longer antennas. This is often in conflict with a desire to have a minimum physical package size for such devices. One technique used to accommodate these conflicting concerns is to use a retracting antenna, such as a retracting whip antenna.
Portable wireless communications devices that include retracting antennas are sometimes required to wirelessly communicate even when the antenna is retracted. An example of such operation is a cellular phone that is kept in a person's pocket with its antenna retracted but that still receives and even transmits status and other information while in the person's pocket with the antenna retracted. Moving a retractable antenna from an extended to a retracted position, and vice versa, generally causes the antenna to change its impedance characteristics. This requires a compromise to be made in impedance matching circuits that couple an RF signal to and/or from the antenna so that acceptable performance is achieved while the antenna is both extended and retracted. This compromise is a particular problem with impedance matching circuits that are used to optimize antenna operation in multiple RF bands. This compromise results in a loss of antenna efficiency when the antenna is in either position compared to the efficiency that could be achieved if impedance matching could be optimized for each position.
Therefore a need exists to overcome the problems with the prior art as discussed above.